olefin-based thermoplastic elastomers are widely used as elastomers of energy-saving and resource-saving type, for a weather strip for automobiles (window frame, door glass run, draining lip, etc.), an automobile interior sheet (door trim material, ceiling material, instrument panel material, etc.), a bumper material, a mudguard material, various sealing materials for building, and the like.
Olefin-based thermoplastic elastomers are described, for example, in Japanese Patent Application Publication No. S53-21021 (Patent Document 1), Japanese Patent Application Publication No. S55-18448 (Patent Document 2), Japanese Patent Application Publication No. S56-15741 (Patent Document 3), Japanese Patent Application Publication No. S56-15742 (Patent Document 4), Japanese Patent Application Publication No. S58-46138 (Patent Document 5), Japanese Patent Application Publication No. S58-56575 (Patent Document 6), Japanese Patent Application Publication No. S59-30376 (Patent Document 7), Japanese Patent Application Publication No. S62-938 (Patent Document 8), Japanese Patent Application Publication No. S62-5913 (Patent Document 9), and the like. A non-crosslinked or crosslinked olefin-based thermoplastic elastomer is selectively used depending on the application.
A well-known olefin-based thermoplastic elastomer composition comprises an ethylene-based copolymer elastomer formed from ethylene, and an α-olefin having 3 to 20 carbon atoms and/or a nonconjugated polyene as an elastomer component. The following findings are reported, for example, in Japanese Patent Laid-open Publication No. H2-60951 (Patent Document 10): a mineral oil softener is blended in such a composition in order to improve workability and to facilitate dispersion of various types of fillers or to increase flexibility and elasticity through reducing hardness; and a mineral oil softener having a viscosity index of 80 or more is preferred because of the superiority in weatherability to other mineral oils.
However, when a paraffin-based mineral oil having viscosity index of 80 or more was used for the olefin-based thermoplastic elastomer composition, its characteristic of flexibility at low temperatures was sometimes deteriorated because of the high pour point of the mineral oil. Moreover, addition of a large amount of mineral oil sometimes caused bleeding-out, which damaged appearance of products, because a wax component contained in the paraffin-based mineral oil had poor compatibility with the olefin-based thermoplastic elastomer composition.
Furthermore, when a naphthene-based mineral oil was used in order to prevent the deterioration of flexibility at low temperatures, the olefin-based thermoplastic elastomer composition became gelled in a short period on exposure to sun light due to sulfur contained in the mineral oil, causing problems of chalking and deterioration of the properties. As described above, when the mineral oil-based softener was used in the olefin-based thermoplastic elastomer composition, there were problems in any of weatherability, flexibility at low temperatures, and stickiness due to the bleeding-out of oil.
Meanwhile, Japanese Patent Laid-open Publication No. 2001-049056 (Patent Document 11) disclosed blending a copolymer liquid synthetic softener that was formed from ethylene and an α-olefin having 3 to 20 carbon atoms and had a number average molecular weight of 400 to 2000, a pour point of −25° C. or lower, and a viscosity index of 120 or more, in place of blending the mineral oil, in the olefin-based thermoplastic elastomer. In practice, however, that blend was accompanied by the following problems: A high ethylene content in the synthetic softener lowered the compatibility of the softener with polypropylene which was a main component of the resin in the olefin-based thermoplastic elastomer composition, thereby deteriorating the fluidity and hence the processability; whereas a low ethylene content in the synthetic softener reduced the compatibility with the ethylene-based copolymer elastomer, possibly causing the bleeding-out of oil particularly in the use at high temperatures, which made the olefin-based thermoplastic elastomer composition sticky.    Patent Document 1: Japanese Patent Application Publication No. S 53-21021    Patent Document 2: Japanese Patent Application Publication No. S55-18448    Patent Document 3: Japanese Patent Application Publication No. S56-15741    Patent Document 4: Japanese Patent Application Publication No. S56-15742    Patent Document 5: Japanese Patent Application Publication No. S58-46138    Patent Document 6: Japanese Patent Application Publication No. S58-56575    Patent Document 7: Japanese Patent Application Publication No. S59-30376    Patent Document 8: Japanese Patent Application Publication No.    Patent Document 9: Japanese Patent Application Publication No. S62-5913    Patent Document 10: Japanese Patent Application Publication No. H2-60951    Patent Document 11: Japanese Patent Laid-open publication No. 2001-049056